Conventionally, various forms of conductive contact members have been used in electrically testing (open/short circuit tests, environmental tests, burn-in tests and so forth) electroconductive patterns of printed circuit boards and electronic components, and have been widely used in contact probes for testing wafers, electric sockets for semiconductor devices in such forms as LGA, BGA, CSP and bare chip, and connectors.
In applications to electric sockets for semiconductor devices, for instance, there is a trend for using higher signal frequencies for semiconductor devices, and frequencies in the order of hundreds of MHz have become very common. In a socket for a semiconductor device which operates under such high frequency signals, the conductive contact member which forms a part of the electrically conductive path for the device is required to have an even lower inductance and resistance. For instance, U.S. Pat. No. 6,043,666 issued Mar. 26, 2000 to T. Kazama discloses a coil spring having a closely wound conical end which serves as a contact member so that the contact member and compression coil spring are integrally combined, and the inductance and resistance are reduced.
In addition to the need to reduce the electric inductance and resistance, it is desired to ensure the positional accuracy of each contact member with respect to the object to be contacted particularly when a large number of such conductive contact members are arranged in a support member to access a large number of points at the same time.
A conductive coil contact member allows the electric inductance and resistance to be minimized, but causes some difficulty in achieving the positional accuracy of its tip with respect to the object to be contacted. The tip is formed by conically winding a coil wire, but the last turn of the coil wire has a certain radius, and the position of the tip of the cone or the highest point of the cone could be anywhere along the last turn which is offset from the axial center of the cone by this radius. In short, the position of the tip of a conically wound contact member is offset from the axial center of the cone by a distance equal to the radius of the last turn of the coil wire.
Such an offset can be reduced by reducing the radius of the last turn, but it is difficult to reduce the radius of a turn beyond a certain limit for a given diameter of the coil wire. If a coil wire having a small diameter is used, it is possible to reduce the radius of the turn, but the desired resiliency or rigidity of the contact member may not be achieved, and the electric inductance and resistance inevitably increase.
U.S. Pat. No. 6,043,666 discloses a conductive coil contact member having each coil wire end formed into a pin extending centrally in the axial direction. Such an arrangement permits the positional accuracy of each tip to be increased without any limit in theory, but becomes impractical when the size of the conductive coil contact member is reduced beyond a certain level.